1. Field of the Invention
The present invention relates to a spin-valve magnetoresistive thin film element which changes in electric resistance according to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is affected by external magnetic fields. More particularly, the present invention relates to a spin-valve magnetoresistive thin film element wherein the pinned magnetic layer is divided into two layers, such that the magnetization (Ferri-state) between the two pinned magnetic layers can be maintained in a thermally stabilized state. The present invention also relates to a thin film magnetic head using this spin-valve magnetoresistive thin film element.
The present invention also relates to a spin-valve magnetoresistive thin film element which changes in electric resistance according to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is affected by external magnetic fields, and particularly relates to a spin-valve magnetoresistive thin film element wherein the magnetization of the pinned magnetic layer can be maintained in a more stabilized state by causing a sensing current to flow in an appropriate direction, and also relates to a thin film magnetic head using this spin-valve magnetoresistive thin film element.
The present invention also relates to a spin-valve magnetoresistive thin film element which changes in electric resistance according to the relationship between the pinned magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is affected by external magnetic fields, and particularly relates to a method for manufacturing a spin-valve magnetoresistive thin film element wherein magnetization control of the pinned magnetic layer can be performed in an appropriate manner by appropriately adjusting the magnetic moment of the pinned magnetic layer, and the direction and size of the magnetic field to be applied during thermal treatment, and also relates to a method for manufacturing a thin film magnetic head using this spin-valve magnetoresistive thin film element.
2. Description of the Related Art
A spin-valve magnetoresistive thin film element is a type of GMR (giant magnetoresistive) element which makes use of the giant magneto resistance effect, and is used for detecting recorded magnetic fields from recording mediums such as hard disks and the like.
The spin-valve magnetoresistive thin film element has several advantages, such as having a relatively simple structure for a GMR element. Further, the spin-valve magnetoresistive thin film element can change resistance under weak magnetic fields.
In its simplest form, the spin-valve magnetoresistive thin film element is comprised of an antiferromagnetic layer, a pinned magnetic layer, a nonmagnetic electrically conductive layer, and a free magnetic layer. FIG. 28 is a cross-sectional view of a known spin-valve magnetoresistive thin film element, viewed from the side opposing a recording medium.
Also, FIG. 29 is a sideways cross-sectional diagram schematically illustrating the spin-valve magnetoresistive thin film element shown in FIG. 28.
Reference numeral 1 denotes a base layer formed of Ta (tantalum) for example, and formed on this base layer 1 is formed an antiferromagnetic layer 2, and further a pinned magnetic layer 3 is formed on the antiferromagnetic layer 2.
The pinned magnetic layer 3 is formed in contact with the antiferromagnetic layer 2, thereby generating an exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface between the pinned magnetic layer 3 and the antiferromagnetic layer 2, and the magnetization of the pinned magnetic layer is pinned in the Y direction in the Figure, for example.
Formed upon the pinned magnetic layer 3 is a nonmagnetic electrically conductive layer 4 formed of Cu or the like, and further formed upon the nonmagnetic electrically conductive layer 4 is a free magnetic layer 5. Formed on either side of the free magnetic layer 5 are hard magnetic bias layers 6 formed of a Co--Pt (cobalt-platinum) alloy for example, and the hard magnetic bias layers 6 are magnetized in the direction X in the Figure, so the magnetization of the free magnetic layer 5 is aligned in the direction X in the Figure. Accordingly, the fluctuation magnetization of the free magnetic layer 5 and the pinned magnetization of the pinned magnetic layer 3 are in an intersecting relationship. Incidentally, reference numeral 7 denotes a protective layer formed of Ta or the like, and reference numeral 8 denotes a lead layer formed of Cu or the like.
With this spin-valve magnetoresistive thin film element, a sensing current flows from the lead layer 8 either in the direction of X shown in the Figure or in the direction opposite to X shown in the Figure, with mainly the nonmagnetic electrically conductive layer 4 as the center. Then, when the magnetization of the free magnetic layer 5 aligned in the direction X in the Figure fluctuates due to magnetic field leaking from the recording medium (such as a hard disk), electric resistance changes according to the relationship between the magnetization of the free magnetic layer 5 and the magnetization of the pinned magnetic layer 3 pinned in the direction Y in the Figure, and a magnetic field leaking from the recording medium is detected by voltage change based on the change in the electric resistance values.
Also, with known arrangements, FeMn alloys, NiO, NiMn alloys, etc., are used for the antiferromagnetic layer 2. Of these examples, using FeMn alloys or NiO as the antiferromagnetic material does not necessitate thermal treatment in order to generate an exchange coupling magnetic field at the interface between the antiferromagnetic layer 2 and the pinned magnetic layer 3, but using NiMn as the antiferromagnetic material does necessitate thermal treatment.
Now, with known arrangements, NiMn alloys, FeMn alloys, NiO, etc., are used as antiferromagnetic materials for the antiferromagnetic layer 2.
However, of these, the blocking temperature of FeMn alloys and NiO alloys in particular is 200.degree. C. or lower, meaning that these materials are lacking in stability. Particularly, in recent years, the number of revolutions of the recording medium and the amount of sensing current flowing from the lead layer 8 have been increasing, and the environmental temperature within the device reaches high temperatures of 200.degree. C. for example, or higher. Accordingly, using an antiferromagnetic material with low blocking temperature as the antiferromagnetic layer 2 of the spin-valve magnetoresistive thin film element reduces the exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the antiferromagnetic layer 2 and the pinned magnetic layer 3. The result is that the magnetization of the pinned magnetic layer 3 cannot be appropriately pinned in the direction Y in the Figure, consequently allowing .DELTA.MR (rate of change of resistance) to drop.
The blocking temperature is determined solely by the antiferromagnetic material comprising the antiferromagnetic layer 2. Thus, even if the structure of the spin-valve magnetoresistive thin film element is improved, the blocking temperature itself cannot be raised.
For example, U.S. Pat. No. 5,701,223 discloses an invention wherein the structure of the pinned magnetic layer is improved and the exchange coupling magnetic field can be improved. However, this invention uses NiO as the antiferromagnetic layer, so the blocking temperature is around 200.degree. C. Thus, even though the exchange coupling magnetic field may be increased at room temperature, the exchange coupling magnetic field of the spin-valve magnetoresistive thin film element becomes smaller while the recording medium is running as the environmental temperature within the device reaches the vicinity of 200.degree. C. or higher. The exchange coupling magnetic field may becomes 0, so no .DELTA.MR can be obtained at all.
On the other hand, NiMn alloys have higher blocking temperatures than NiO or FeMn alloys, but the properties of these alloys, such as corrosion-resistance and the like are poor, so an antiferromagnetic material with even higher blocking temperatures and excellent properties thereof such as corrosion-resistance is being demanded.
Also, as described above, the sensing current flows from the lead layer 8 with mainly the nonmagnetic electrically conductive layer 4 having low ratio resistance as the center, so a sensing current magnetic field is formed by the corkscrew rule because of the sensing current that is caused to flow. This sensing current magnetic field affecting the pinned magnetization of the pinned magnetic layer 3.
For example, as shown in FIG. 29, the magnetization of the pinned magnetic layer 3 is directed in the direction of Y in the Figure. But if the sensing current magnetic field generated by causing sensing current to flow is directed in the direction opposite to Y in the Figure at the portion of the pinned magnetic layer 3, the direction of the pinned magnetization of the pinned magnetic layer 3 and the direction of the sensing current magnetic field do not match, so the pinned magnetization is affected by the sensing current magnetic field and wavers. This problem in that the state of magnetization becomes unstable.
Particularly, if an antiferromagnetic material such as an NiO or FeMn alloy which produces only a small exchange coupling magnetic field (exchange anisotropic magnetic field) generated at the interface between the pinned magnetic layer 3 and the antiferromagnetic layer 2, and which has low blocking temperature, is used for the antiferromagnetic layer 2, the deterioration of the pinned magnetism at the pinned magnetic layer 3 is marked if the pinned magnetization direction of the pinned magnetic layer 3 and sensing current magnetic field direction are facing opposite directions, and destruction may occur such as the inversion of pinned magnetism.
In recent years, there is a trend to use a large sensing current in order to deal with higher densities. However it is known that causing a sensing current of 1 mA to flow generates a sensing current magnetic field of approximately 30 (Oe), and further that the element temperature rises by about 15.degree. C. Thus, if several tens of mA of the sensing current is caused to flow, this will result in a sudden rise in the temperature of the element, and generate a massive sensing current magnetic field.
Accordingly, in order to improve the thermal stability of the pinned magnetization of the pinned magnetic layer 3, an antiferromagnetic material with a high blocking temperature and which produces a large exchange coupling magnetic field (exchange anisotropic magnetic field) at the interface between the pinned magnetic layer 3 and the antiferromagnetic layer 2 needs to be selected, and the sensing current needs to be directed in an appropriate direction so the magnetization of the pinned magnetic layer 3 is not destroyed by the sensing current magnetic field.
U.S. Pat. No. 5,701,223 discloses an invention wherein the pinned magnetic layer is divided into two layers and the magnetization of the two pinned magnetic layers is in an antiparallel state, whereby a large exchange coupling magnetic field can be obtained.
However, the antiferromagnetic layer disclosed here is NiO, and NiO has a low blocking temperature of around 200.degree. C., and only a small exchange coupling magnetic field (exchange anisotropic magnetic field) is generated at the interface between the pinned magnetic layer and the antiferromagnetic layer.
Particularly, in recent years, there is a trend to increase the rotating speed of the recording medium and increase the sensing current in order to deal with higher densities, which causes the environmental temperature within the device to rise. Thus, if NiO is used for the antiferromagnetic layer, the exchange coupling magnetic field is smaller, meaning that it is difficult to appropriately carry out magnetization control of the pinned magnetic layer.
On the other hand, NiMn alloys have a higher blocking temperature than the NiO, and the exchange coupling magnetic field (exchange anisotropic magnetic field) is also greater. Also, X--Mn alloys (wherein X is Pt, Pd, Ir, Rh, Ru) using elements of the platinum group have come into focus as an antiferromagnetic material which has blocking temperature around that of NiMn alloys, a large exchange coupling magnetic field, and corrosion-resistance far better than NiMn alloys.
Employing such X--Mn alloys using elements of the platinum group as the antiferromagnetic layer, and further dividing the pinned magnetic layer into two layers should facilitate the obtaining a greater exchange coupling magnetic field as compared to using NiO for the antiferromagnetic layer.
Presently, such X--Mn alloys using elements of the platinum group need to be annealed in a magnetic field (thermal treatment) following formation of the film, in order to generate an exchange coupling magnetic field at the interface between the pinned magnetic layer and the antiferromagnetic layer, as is true with the case of NiMn alloys, as well.
However, unless the size and direction of the magnetic field applied during the thermal treatment, and the magnetic moment (saturation magnetization Ms.cndot.film thickness t) of the two divided pinned magnetic layers are appropriately adjusted, the magnetization of the two divided pinned magnetic layers cannot be pinned in a stable antiparallel state. Also, particularly, with so-called dual spin-valve magnetoresistive thin film elements (wherein the pinned magnetic layers are formed above and below the free magnetic layer with the free magnetic layer as the center thereof), the magnetization direction of the two pinned magnetic layers formed above and below the free magnetic layer must be appropriately controlled, or .DELTA.MR (the rate of resistance change) drops, causing problems such that only a small reproduction output can be obtained.